Osman’s beylik ate Byzantium one fortress at a time
After Greeks clawed Constantinople back from Latin rule in 1261, the rebuilt empire faced Serbian pressure, restless Latin duchies, and Turkish ghazi beyliks filling the vacuum of the dying Sultanate of Rum. One of those beys, Osman I, founded the line that would extinguish Byzantine independence.
Komnenian emperors had once held a firm Danube frontier; by the late thirteenth century that shield was gone and danger reached the capital’s suburbs. Michael VIII blinded young co-emperor John IV to lock his own hold on the throne, sparking outrage he tried to soothe with a new patriarch and diplomacy. Around him, Anatolian warriors carved fiefs from both Byzantine and Seljuk land, and Osman’s holdings proved the most durable threat among many Turkish beys.
Andronikos’s later government compounded the wound: debasing the hyperpyron cheapened the economy, tax relief for landed magnates shifted burdens onto lesser knightly classes, and short-sighted choices left the state unable to fund adequate defence. Latin princes still dreamed of retaking Constantinople for their lost empire, while Serbian expansion pressed from the Balkans, trapping the restored Roman state between Catholic nostalgia and Orthodox rivals.
The Anatolian collapse was swift. Within 90 years of Osman founding his beylik, Byzantium had lost all of Asia Minor, and by 1400 Thrace had gone too. A relief army was routed at Pelekanos on 10 June 1329, Nicaea surrendered in 1331, and Nicomedia fell in 1337 after a siege begun in 1333. In 1338 Orhan took Skoutarion, the first Ottoman foothold in view of the capital, even as Andronikos III briefly regained Thessaly, Epirus, Chios and Lesbos.
Civil wars finished the job. When Andronikos III died in 1341, leaving ten-year-old John V, a feud inside the regency handed John Cantacuzenus the capital in 1347, and rival claimants began hiring Turkish troops. Orhan's men occupied Tzimpe in 1352 and Gallipoli in 1354, securing a bridgehead in Europe. Murad I then destroyed a Serbian army at Maritsa on 26 September 1371, and John V went as far as professing the Catholic faith in St Peter's in search of Western help.
Source: Byzantine–Ottoman wars
